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Use WildcardType in place of a type variable in pretypeArgs #3974

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Merged
merged 1 commit into from
Feb 12, 2018
Merged

Use WildcardType in place of a type variable in pretypeArgs #3974

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2 changes: 1 addition & 1 deletion compiler/src/dotty/tools/dotc/typer/Applications.scala
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Original file line number Diff line number Diff line change
Expand Up @@ -1459,7 +1459,7 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
fn.get.isInstanceOf[untpd.Match] &&
formalsForArg.exists(_.isRef(defn.PartialFunctionClass))
val commonFormal =
if (isPartial) defn.PartialFunctionOf(commonParamTypes.head, newTypeVar(TypeBounds.empty))
if (isPartial) defn.PartialFunctionOf(commonParamTypes.head, WildcardType)
else defn.FunctionOf(commonParamTypes, WildcardType)
overload.println(i"pretype arg $arg with expected type $commonFormal")
pt.typedArg(arg, commonFormal)(ctx.addMode(Mode.ImplicitsEnabled))
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18 changes: 18 additions & 0 deletions tests/pos/overloaded.scala
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Expand Up @@ -29,22 +29,40 @@ object overloaded {
val r2 = map(x => x.toInt)
val t2: Seq[Int] = r2

val rp1 = map { case x => x.toUpper }
val tp1: String = rp1
val rp2 = map { case x => x.toInt }
val tp2: Seq[Int] = rp2

def flatMap(f: Char => String): String = ???
def flatMap[U](f: Char => Seq[U]): Seq[U] = ???
val r3 = flatMap(x => x.toString)
val t3: String = r3
val r4 = flatMap(x => List(x))
val t4: Seq[Char] = r4

val rp3 = flatMap { case x => x.toString }
val tp3: String = rp3
val rp4 = flatMap { case x => List(x) }
val tp4: Seq[Char] = rp4

def bar(f: (Char, Char) => Unit): Unit = ???
def bar(f: Char => Unit) = ???
bar((x, y) => ())
bar (x => ())
// bar { case (x, y) => () } // error: cannot test if value types are references
bar { case x => () }

def combine(f: (Char, Int) => Int): Int = ???
def combine(f: (String, Int) => String): String = ???
val r5 = combine((x: Char, y) => x + y)
val t5: Int = r5
val r6 = combine((x: String, y) => x ++ y.toString)
val t6: String = r6

// Errors: The argument types of an anonymous function must be fully known
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@odersky Is this intended? Should I open an issue for it?

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I think it's fine; we don't look inside tuples here. What does scalac say?

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Tested on Scala 2.13.0-M2:

[error] constructor cannot be instantiated to expected type;
[error]  found   : (T1, T2)
[error]  required: Char
[error]   bar { case (x, y) => () }
[error]              ^

[warn] match may not be exhaustive.
[warn] It would fail on the following input: (_, _)
[warn]   val rp5 = combine { case (x: Char, y) => x + y }
[warn]                     ^

[warn] match may not be exhaustive.
[warn] It would fail on the following input: (_, _)
[warn]   val rp6 = combine { case (x: String, y) => x ++ y.toString }
[warn]                     ^
[warn] two warnings found

In two out of tree of the cases scalac is able to find the correct overload. It emits a spurious exhaustivity warning though

// val rp5 = combine { case (x: Char, y) => x + y }
// val tp5: Int = rp5
// val rp6 = combine { case (x: String, y) => x ++ y.toString }
// val tp6: String = rp6
}